A superjunction semiconductor device, such as a superjunction MOSFET, includes a plurality of transistor cells each including a drift region of a first doping type, and a compensation region of a second doping type complementary to the first doping type. The compensation region adjoins the drift region so that there is a pn junction between the drift region and the compensation region. This pn junction is substantially perpendicular to a current flow direction of the semiconductor device. In a MOSFET, another pn junction is formed between the drift region and a body region, and the compensation region is usually coupled to the body region. When the pn junction between the body region and the drift region is reverse biased, which is when the MOSFET is in an off-state, the pn junction between the drift region and the compensation region is also reverse biased. Thus, an electric field in the drift region has substantially two components, namely a first component resulting from the voltage that reverse biases the pn junction between the body region and the drift region, and a second component resulting from the voltage that reverse biases the pn junction between the compensation region and the drift region.
The compensation region has a first end facing away from the pn junction between the body region and the drift region. In order to increase a dynamic robustness it is desirable to design the drift region and the compensation region such that a maximum electric field occurs in the drift region at a position between the first end of the compensation region and the pn junction between the body region and the drift region. For example, this position can be adjusted through an adapted vertical resolved doping profile of the compensation region.
A conventional process for producing a drift region and an adjoining compensation region includes producing a layer stack with a plurality of epitaxially grown layers of a first doping type, wherein dopant atoms of a second doping type are introduced into each of these layers at positions that are located one above the other in the layer stack. After these layers have been produced, an annealing process causes the implanted dopant atoms to diffuse in the individual layers, thereby forming pile shaped compensation regions of the second doping type in the layer stack. Those regions of the epitaxial layers that keep the basic doping of the first doping type form the drift region. In this process, a doping concentration of the compensation region can be adjusted through a dopant dose that is introduced into the individual epitaxial layers. A fine adjustment of the doping concentration is, in particular, possible when thin epitaxial layers are produced. However, this increases the number of epitaxial layers to be produced. Further, in a device where a plurality of transistor cells are formed, the diffusion of the dopants into the epitaxial layers makes it difficult to reduce a distance (often referred to as “pitch”) between neighboring transistor cells without taking the risk that the compensation regions of two neighboring cells eliminate the drift region between them.